SLUUCW9 User guide

SLUUCW9 December 2023 BQ76972

4.10.1 Fixed Offset Adjustment

Fixed offset adjustment is performed by the host processor subtracting fixed per-cell offset values from the reported cell measurement results to obtain finalized cell measurement values.

The per-cell offset values are the same for all devices and do not require measurement of each device on the customer production line.

Two sets of offset adjustment values are provided:

One set optimized for LFP cells, with cell voltages ranging from 2 V to 3.7 V
A second set optimized for Li-ion cells, with cell voltages ranging from 2 V to 4.5 V

The two sets of optimized offset values are described below.

Table 4-9 Fixed Offset Adjustment Values Optimized for LFP Cells

Offset value	Cell 1 Offset	Cell 2 Offset	Cell 3 Offset	Cell 4 Offset	Cell 5 Offset	Cell 6 Offset	Cell 7 Offset	Cell 8 Offset
Offset (mV)	-0.6	-0.8	-0.8	-0.8	-0.5	-0.6	-0.6	-0.6

Offset value	Cell 9 Offset	Cell 10 Offset	Cell 11 Offset	Cell 12 Offset	Cell 13 Offset	Cell 14 Offset	Cell 15 Offset	Cell 16 Offset
Offset (mV)	-0.3	-0.4	-0.1	-0.1	-1.3	-1.1	-1.2	-0.7

Table 4-10 Fixed Offset Adjustment Values Optimized for Li-ion Cells

Offset value	Cell 1 Offset	Cell 2 Offset	Cell 3 Offset	Cell 4 Offset	Cell 5 Offset	Cell 6 Offset	Cell 7 Offset	Cell 8 Offset
Offset (mV)	-0.7	-1.0	-0.9	-1.0	-0.6	-0.7	-0.8	-0.9

Offset value	Cell 9 Offset	Cell 10 Offset	Cell 11 Offset	Cell 12 Offset	Cell 13 Offset	Cell 14 Offset	Cell 15 Offset	Cell 16 Offset
Offset (mV)	0.2	0.0	-0.2	-0.4	1.1	0.8	0.7	0.1

During operation, the cell measurements are read from the BQ76972 as Cell 1 Voltage(), Cell 2 Voltage(), and so on. The host then calculates adjusted values for each cell voltage:

Final Cell 1 Voltage = Cell 1 Voltage() - Cell 1 Offset
Final Cell 2 Voltage = Cell 2 Voltage() - Cell 2 Offset
and so on

All devices use the same 16 values for Cell 1 Offset, for Cell 2 Offset, and so on.